Hey Burt Gummer, Ford is testing out a truck that might finally be the perfect replacement for your K5 GMC Jimmy. The CarBuzz spies have spotted what might be the heaviest Tremor yet. It's a Ford F-350 wearing a color we haven't seen before and tires that put the super in Super Duty. This F-350 prototype is wearing 37-inch tires, showing that the Blue Oval is looking to make its big pickup even bigger and meaner than ever. A Strange Blend Of Parts With 37-inch Tires CarBuzz/Valnet This prototype truck is a strange blend of bits and bobs and bumpers and tailgates from the Ford parts bin, which makes sense if you're developing a prototype but looks extremely strange on the road. Take a close look at the front end, to start, where the lower section of the headlights as well as the fog lights are covered with tape. Not camouflage tape like we're used to, but what looks more like gaffer tape completely covering the lenses.Step back and this is still a very different take on the Super Duty's nose. What looks like a blacked-out headlight trim is just more tape. There is also tape covering the entire third brake light (but not the camera) and the reversing lights on the taillight assembly.It has a King Ranch tailgate trim without chrome, along with Tremor wheels and running boards. The desert sand paint is a factory Ford color, but it's the paint from the Ranger Super Duty sold in Australia, not a color Ford normally sells stateside. To round up the confusion, the fender vent is the one from a Lariat trim, but with the chrome removed. It's not the Black Appearance Package trim, either, though the front grille is. Is This A Super Tremor? CarBuzz/Valnet Combine all of those changes with the faded flag decal in the back window, and we would have said this was a custom and not a Ford factory prototype. But with a Michigan manufacturer plate, a Ford Proving Ground sticker in the window, and the expert knowledge of our spies, we know that it's at least in and out of Ford's garages. And it's not the only truck like this running around town.So what is this beast? A Super Duty Raptor would be interesting, but even if Ford was working on one, we don't think it would be this mild. Those are stock-looking front and rear springs, and Tremor shocks. That's not Raptor style.CarBuzz/Valnet Is Ford working on a 37-inch tire package for Super Duty? That's possible, and it would justify the extra development process. When Ford added 37s to the F-150 Raptor, it needed to install a new rear cross member and support so the tall diameter tires could fit. It even needed a strengthened frame to handle the extra weight moving up and down.There is another other possibility, and the window flag is pushing us in this direction. This could be a truck built for a film shoot of some kind. A TV series or a movie where the desert paint looks cool and reflections from the lights are bad for the camera. Or, it could be an indication of some burly special edition truck not unlike those we see from Ram, adorned with flag decals. This is all speculation on our part, so keep that in mind.Stay tuned. As soon as Ford makes anything official, we'll be here to keep you posted.Ford F-350 Super Duty spy photo (19)